| 摘要 |
FIELD: electricity.SUBSTANCE: according to the method for determination of frequency F the digital signals of all three phases Ua(t), Ub(t), Uc(t) of industrial three-phase voltage measured in the moments t, where i - the whole value, digitized with the period dt = (t-t) are used. And the value dt is much less than the period T of the maximum frequency Fb = 1/T of the measurement range, dt<<T. Meanwhile the projection Ux(t) to the axis X of the rotating field U(t), created by three phases Ua(t), Ub(t), Uc(t) of industrial three-phase voltage, using the formulathe projection Uy(t) to the axis Y of the rotating field U(t) - Uy(t) = (2·Ua(t)-Ub(t)- Uc(t))/2, the module of the rotating field U(t) -are detrmined. The dependence from the time tof the phase increment d?of the rotating field U(t) within the interval dt = (t-t) is determined according to the formula: |d?| = |?(t)-?(t)| = arccos{[Ux(t)·Ux(t)+Uy(t)·Uy(t)]/[U(t)·U(t)]}, and the sign of d?is determined according to the following algorithm: if |Ux(t)|?| Uy(t)|, then the sign of d?is equal to the sign of the value Uy(t)·[Ux(t)-Ux(t)], if |Ux(t)>|Uy(t)|, then the sign of d?is equal to the sign of the value Ux(t)·[Uy(t)-Uy(t)]. The average value of the frequency F(t) for the period n·dt at the moment tis determined by the formulawhere n is integer value.EFFECT: improvement of accuracy of determination of three-phase voltage frequency.3 dwg |
